1. Field of the Invention
The invention relates to a coupling device, and more particularly to a coupling device transmitting a circular polarized wireless signal.
2. Description of the Related Art
FIGS. 1a and 1b show a conventional coupling device 1 for transmitting a circular polarized wireless signal, which comprises a substrate 10, a radiator 20 and a ground layer 30. The substrate 10 comprises a first surface and a second surface. The first surface is opposite to the second surface. The radiator 20 is disposed on the first surface. The ground layer 30 is disposed on the second surface. The radiator 20 is rectangular, and comprises a lead angle 21. FIG. 1b is a sectional view along direction A-A of FIG. 1, wherein a coaxial cable 40 is electrically connected to the coupling device 1, and a signal line 41 passes the substrate 10 to be connected to the radiator 20.
Conventional coupling device 1 provides an axial ratio bandwidth of about 3˜5%, which, however, cannot transmit wireless signals having various resonance directions.